The red blood cells or erythrocytes in donor blood have a certain life span. Actually, human blood contains more or less equal portions of red blood cells of ages between about 0 and 120 days. Thus, in any given sample, there is a certain percentage of younger blood cells or so-called neocytes and a certain percentage of older cells called gerocytes. Also, human blood contains a relatively large amount of iron, on the order of 108 mg/dl of red cells. Furthermore, the iron content is relatively uniform regardless of the average cell age of the blood sample. There are some patients, those suffering from chronic anemias for example, who depend upon repeated blood transfusions for their survival. Indeed, they may receive donor blood at such a rate that their systems are unable to entirely dispose of the iron content of that blood with the result that the patients suffer from iron overload and may die from complications resulting from that cause.
Since the contribution to iron overload is the same from the oldest transfused red cells which survive only a few hours as from the youngest ones which circulate in the body for months, it has been obvious for some time that a blood transfusion for patients such as this would be much more effective in terms of the ratio of physiological benefit to iron overload if the older red cells were removed from the donor blood and only the younger cells administered to the patient.
It has also been recognized that the red cells in donor blood have a certain density distribution. Indeed, it turns out that the older red blood cells are more dense than the younger ones. Using this knowledge, attempts have been made to separate the red cells in a donor sample according to their densities so as to segregate the younger red cells or neocytes from the older cells or gerocytes. Some such attempts, described for example in the following publications (copies of which are attached hereto), involve centrifuging the donor blood:
Murphy, John R., "Influence of temperature and method of centrifugation on the separation of erythrocytes", J. Lab. Clin. Med., August, 1973, pp. 34-341; Corash, Lawrence M., et al, "Separation of erythrocytes according to age on a simplified density gradient", J. Lab. Clin. Med., July, 1974, pp. 147-151; Piomelli, Sergio, et al, "Separation of younger red cells with improved survival in vivo: An approach to chronic transfusion therapy", Proc. Natl. Acad. Sci. USA 75 (1978), pp. 3474-3477; and Vettore, Luciano, et al, "A New Density Gradient System for the Separation of Human Red Blood Cells", American Journal of Hematology, 8:291 at Volume 8 (1980), pp. 291-297.
The usual technique for separating whole blood in accordance with the density of the blood fractions is to place the blood sample in a container and spin the container about an axis perpendicular to the container axis at a high speed to subject the container contents to a centrifugal force on the order of 2,000 G. The force exerted on the contained blood sample causes the heaviest, most dense blood fractions such as the red cells to accumulate at the bottom or closed end of the container distal from the spin axis, while the less dense fractions, such as the blood plasma, accumulate at zones in the container progressively closer to the spin axis. Typical apparatus for effecting density separation of blood fractions by centrifuging are disclosed in the above mentioned Murphy article, as well as in the following U.S. patents:
______________________________________ 3,064,647 Earl 3,935,113 Ayres 3,750,645 Bennet et al 3,945,928 Ayres 3,800,947 Smith 4,187,861 Heffernan 3,887,464 Ayres 4,189,385 Greenspan ______________________________________
As described in some of these prior references, the Ayres patents for example, the centrifuged container defines upper and lower chambers separated by a check valve. The whole blood is placed in the upper chamber and the container is accelerated up to high speed. Under the high G force, the heavier blood fractions tend to find their way to the bottom of the upper chamber and pass through the check valve into the lower chamber. Such apparatus does effectively separate whole blood into its gross fractions; i.e. the plasma having a density of about 1.01 g/cc is separated from the blood cells having an average density of 1.07 g/cc. This is because that density difference is quite significant at centrifuge speeds. Also, according to Murphy and others, there is apparently also some separation of the red blood cells themselves in accordance with a density gradient.
While Murphy and others have drawn off samples of the centrifuged blood at different zones in a container using quite complicated and time-consuming mixing and aspirating techniques in order to test and verify that some separation of cells according to age has occurred, until now there has been no effective way of readily segregating or partitioning the younger red blood cells from the older ones in a sterile environment so that the younger cells would be available for immediate transfusion to a needy patient.